The invention, in some embodiments, relates to the field of global navigation satellite systems, and more particularly to the field of methods and devices for identifying whether a satellite in a global navigation satellite system has a line of sight to a specific global navigation satellite systems receiver (LOS satellite) or does not have a line of sight to the global navigation satellite systems receiver (NLOS satellite).
Global Navigation Satellite Systems (GNSS) provide autonomous geo-spatial positioning, typically including global coverage. A global navigation satellite system allows an electronic receiver to determine its own position, namely longitude, latitude, and altitude, to within a few meters, using ephemeris data and time signals transmitted by radio from one or more satellites.
A GNSS receiver approximates its position by interpolating the signal from each navigation satellite, and specifically the precise coordinates of the satellite contained in the ephemeris data and the time stamps received from the satellite, into a pseudorange, indicating a region to which the signal from the satellite could travel in the specified time duration.
Using the location and pseudorange of at least four satellites, the GNSS receiver computes its location by intersecting the pseudoranges to obtain a user position. The position is generally provided to a user as a position region, for example a position circle having a calculated center point indicating the most likely position of the receiver, and a radius that indicates an estimated error. Mathematically, four pseudoranges are sufficient to determine the position of the receiver with a reasonable error.
Disregarding topography and terrestrial objects on the Earth's surface, most global navigation satellite systems, such as GPS, GLONASS, and Galileo, have satellite coverage that ensures that a receiver on Earth has simultaneous lines of sight (LOS) to at least four satellites and can therefore accurately determine its position.
When the line of sight to a number of satellites is blocked, the accuracy of the calculated position may decrease. For example, in many cities, tall buildings or other obstacles form an urban canyon where sky visibility is greatly limited. It is very common for a GNSS device operating in an area of this sort to be surrounded by obstacles which block the line of sight to most, if not all, otherwise-visible GNSS satellites.
As mentioned above, at least four sufficiently strong signals from four line-of-sight satellites are required for accurate position determination. Therefore, knowing whether or not a specific GNSS satellite has a line of sight to a GNSS receiver may have a great effect on the accuracy of the position calculated by the GNSS receiver. Several uses for identification of GNSS satellites as LOS satellites or NLOS satellites are known, such as those described in U.S. Patent Application Publication No. 2010/0079332 and in PCT patent application PCT/IB2011/055899 filed 22 Dec. 2011 and published as WO 2012/085876 of an Inventor.